Should I negotiate my severance? - 14 months and counting

I was offered 3 weeks of severance after 3 years as an HR coordinator, and I have a few days to sign. There is a non-disparagement clause. Did anyone negotiate and succeed?

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.